Band clamps are commonly used for connecting pipes, hoses, and other tubular members together, such as exhaust pipes of an automotive exhaust system. Such connections are typically constructed in a telescopic overlap joint or in an end-to-end butt joint of two tubular members. To be effective, the connection between the tubular members should provide a suitable fluid-tight seal to prevent leakage. The connection should also have a high degree of mechanical strength and be capable of easy disassembly.
A conventional band clamp includes a band defined by a cylindrical body portion that circumscribes tubular members to be joined. The cylindrical body terminates in opposed, radially extending connection flanges, which are loosened or drawn together around the tubular members by a fastener extending transversely through the flanges. As the fastener is tightened, the opposed flanges are cinched together, thereby applying a strain on the band. This strain creates a radially-directed, compressive clamp load on the tubular members. A reaction member may be provided between the flanges to provide a more even distribution of radial forces on the tubular members as the band is cinched by the tightening of the fastener. In any case, the fastener should be capable of exerting consistent fastening forces that draw the flanges of the band together to impart consistent clamp loads from the band to the tubular members.
Some conventional band clamp designs do not always yield consistent clamp loads—especially when tolerance stackups of band clamp components yield interference conditions when fastening the band clamp. An exemplary conventional band clamp 210 and associated bolt 248 are depicted in prior art FIGS. 6 through 9. As shown in FIG. 6, the bolt 248 includes a head 256 defining one end of the bolt 248, and a cylindrical shank 276 that extends longitudinally away from the head 256 and terminates in an opposite end of the bolt 248. The shank 276 includes a slotted neck 280 with close-ended slots 281, a threaded body 284 of relatively reduced diameter compared to the slotted neck 280, and a conical transition 286 provided between the neck 280 and body 284. As shown in FIG. 7, the shank 276 extends through opposed flanges 226, 228 of a band 216 and through a reaction member 242 positioned between the flanges 226, 228, wherein the slotted neck 280 is adapted for interference fit through the reaction member 242 to enable pre-assembly of the bolt and reaction member onto the flange 228 in a manner that will prevent the bolt from inadvertently slipping off the flange. Prior to tightening the nut 252 onto the bolt 248, there is clearance between the shank 276 and a top of an aperture 272 in the flange 226, as depicted in FIG. 7. As the nut 252 is tightened, however, the top of the aperture 272 is drawn closer to the shank 276, as depicted in FIG. 8. Under some circumstances, such as maximum material conditions of the bolt 248 and band 216, the top of the aperture 272 of the flange 226 initially contacts the threaded body 284 instead of the slotted neck 280, as depicted in FIG. 9. As the nut 252 is further tightened, the top of the aperture 272 of the flange 226 of the band 216 substantially interferes with and traverses the conical transition 286 between the different diameters of the body 284 and neck 280. Under this interference condition, rundown torque applied to the nut 252 tends to fluctuate, thereby resulting in inconsistent nut torques, which translate into unpredictable clamp loads. In turn, unpredictable clamp loads lead to variable results in joint strength.